CN114492234A - Dynamic floating type fan surface rainwater distribution and rainwater load calculation method - Google Patents

Abstract

The invention belongs to the technical field of computational fluid mechanics, and particularly relates to a method for calculating rainwater distribution and rainwater load on the surface of a dynamic floating type fan. The method comprises the steps of measuring the wind speed, the wind pressure and the wind direction of a wind field around a dynamic floating type fan, and constructing a wind field calculation domain in a stable state by taking measured data as boundary conditions; measuring the rainfall intensity of the offshore area of the working position of the dynamic floating type fan, and injecting a rain phase into a numerical wind field; constructing a wind and rain field SRF calculation system, and solving a wind and rain coupling effect control equation; calculating to obtain surface rainwater distribution based on rainfall event observation data; and calculating the impact force of the rainwater on the surface infinitesimal area of the fan on the collision with the fan, and further integrating the whole surface of the fan to obtain the surface rain load of the fan. The method can be used for calculating the rain load of a static building and calculating the rain load of a fan with dynamic characteristics.

Description

A calculation method of rainwater distribution and rain load on the surface of a dynamic floating fan

technical field

The invention belongs to the technical field of computational fluid mechanics, and in particular relates to a method for calculating the rainwater distribution and rain load on the surface of a dynamic floating fan.

Background technique

WAR (Wind And Rain) refers to the phenomenon that raindrops falling vertically under the action of wind have a horizontal velocity vector. WAR is one of the important sources of moisture that affects the damp-heat performance and durability of external surfaces such as machinery and buildings. It will not only produce additional forces on the object to be acted upon and affect its performance, but also lead to some undesirable effects in surface physics. phenomena such as frostbite on the exterior wall surface, erosion of materials. For floating fans, due to the particularity of their environment, they often work under the combined effect of wind and rain. Therefore, the WAR phenomenon has a significant impact on the mechanical wear and work efficiency of the fans. At the same time, the WAR facade distribution It plays an important role in promoting the waterproof design of objects and buildings, the development of waterproof materials, and the research on temperature and humidity performance. Therefore, it is of great significance to determine the surface rainwater distribution and rain load characteristics of the fan in the rotating state for floating fans.

In response to this problem, the inventor found the following deficiencies based on the prior art method:

There are currently three methods for estimating WAR rainwater distribution and loading effects on building surfaces: (1) measurements, (2) semi-empirical methods, and (3) computational fluid dynamics (CFD) methods.

First, the measurement of object facade WAR is difficult, time-consuming, and prone to errors, and they are also limited by the meteorological conditions during the experiment.

Second, semi-empirical methods are fast and easy to use, but they only give an approximation of WAR strength, not detailed information. Furthermore, semi-empirical methods cannot reliably account for all factors affecting WAR strength, especially in multi-building environments.

Third, the current CFD method for the calculation of rainfall conditions adopts the Lagrangian particle tracking method (LPT model) based on Euler two-phase flow, which requires tracking thousands of raindrops on a fine computing grid to obtain accurate results. Therefore, the computational cost is beyond the reach of many researchers. The researchers had to carefully define the droplet injection locations for each droplet diameter so that they covered the entire façade. This step must be repeated for different reference wind speed and reference wind direction values. Furthermore, this method requires computations in very small time steps to obtain accurate results. Therefore, all the steps of LPT, i.e. preprocessing, solving and postprocessing, are very time-consuming. This is mainly applicable when the researcher has sufficient time and the researcher has sufficient computing resources. Furthermore, the current research on CFD methods for wind and rain conditions only focuses on static buildings.

Therefore, for wind turbines with dynamic characteristics under wind and rain conditions, an accurate, efficient and more applicable rain load calculation method is still waiting.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a method for calculating the rainwater distribution and rain load on the surface of the dynamic floating fan.

A method for calculating the rainwater distribution and rain load on the surface of a dynamic floating fan, characterized in that it comprises the following steps:

Step 1: Measure the wind speed, wind pressure and wind direction of the wind field around the dynamic floating fan, and use the measured data as boundary conditions to construct a steady-state wind field calculation domain;

The governing equation of the wind field calculation domain in a steady state is as follows:

Among them, x _i and x _j represent the displacement in the i and j directions respectively; u _i and u _j represent the average wind speed in the i and j directions respectively; ρ _a represents the density of the air; p is the pressure of the air; K represents the turbulent kinetic energy ;ε is the turbulent dissipation rate; τ _ij is the Reynolds stress; μ is the air viscosity; μ _t is the air turbulent viscosity; G _K is the turbulent kinetic energy gradient generated by the average velocity; C _μ , C _2ε , C _1ε and σ _ε are all constant;

Step 2: Measure the rainfall intensity R _h in the offshore area where the dynamic floating fan works; on the basis of the known rainfall intensity, determine which raindrops of different sizes are composed of raindrops under the rainfall intensity R _h and the raindrops of different sizes fall Velocity; different continuous rain phases composed of raindrops of different sizes are added to the top and inlet surfaces of the steady-state wind field calculation domain to construct an Euler multiphase field. The phase fraction is used as the boundary condition of the Euler polyphase field;

Since the falling process of raindrops can be regarded as a process of first acceleration and then uniform velocity, the raindrops will maintain a constant final velocity before reaching the ground, so the initial velocity of the rain phase on the boundary conditions of the computational domain is the final velocity of the raindrops V _k (d _k ), d _k is the raindrop diameter of the k-th phase rain, V _k (d _k ) represents the raindrop velocity of the k-th phase rain with a diameter of d _k ; the calculation method of the rain phase fraction α _k is:

等于零，当正常的风速速度矢量指向计算域时，雨相分数α_k的值等于零；利用此边界条件，雨和外墙壁、风机表面之间的相互作用就可以不用被考虑，雨滴一旦到达壁边界就离开该区域，所以就可以忽略其他因素的能量损失；Set the boundary conditions for the rain phase on the fan surface, ground and outlet as: the fractional gradient of the rain phase when the normal wind speed velocity vector is pointed out from the computational domain

is equal to zero, when the normal wind velocity vector points to the computational domain, the value of the rain phase fraction α _k is equal to zero; using this boundary condition, the interaction between the rain and the outer wall and the fan surface can not be considered, once the raindrops reach the wall boundary leave the area, so the energy loss of other factors can be ignored;

Step 3: Simulate the process of the dynamic floating fan from starting to maintaining a steady state in wind and rain, using a single rotating reference system method, that is, the fan does not move, the coordinate system rotates, and the coordinates in the coordinate system are transformed, and then the computational domain solve;

The rain phase and the wind phase are combined, and the calculation adopts the assumption of one-way coupling, that is, the wind acts on the rain in one direction; the rain phase is considered as a continuum, and each rain corresponds to different levels of raindrop sizes; for each rain phase, the injected After reaching the wind, solve the following continuity and momentum equations when coupled with the wind phase mononomially to obtain the rain phase fraction and velocity field information;

是风相速度矢量，

是雨相速度矢量；where α _k ′ is the rain fraction of the kth phase rain after the wind phase and rain phase are coupled in the computational domain; ρ _w is the raindrop density; g is the acceleration of gravity; C _d is the drag coefficient; Re _R is the relative Reynolds number,

is the wind phase velocity vector,

is the rain phase velocity vector;

Step 4: Calculate the surface rainfall distribution based on the rainfall event observation data;

直接相关，两者计算公式如下：The parameter that defines the distribution of rainwater on the outer surface of the building under the action of wind and rain is the capture ratio, which is defined as the ratio of the rain intensity under the action of wind to the rain intensity on the horizontal plane, and the size of the global capture ratio η is related to the specific capture ratio of each rain phase.

Directly related, the two calculation formulas are as follows:

Among them, u(k) is the final calculated end-impact velocity vector of the kth phase rain; f _h (d _k ) is the size probability distribution value of the rain phase with a diameter of d _k of the kth phase on the horizontal plane under the rainfall intensity R _h ;

Step 5: Calculate the impact force F of the rain on the fan surface micro-element area Δ _s , and then integrate the overall surface of the fan to obtain the rain load on the fan surface;

The impact force of rain on the fan surface micro-element area Δ _s is:

F=ρ _w ηR _h Δ _s u

Among them, u is the combined velocity of the terminal velocity of all rain phases before hitting the fan wall.

The beneficial effects of the present invention are:

The invention couples the Euler multiphase model with the multiple rotating reference frame (SRF) and the collision theory, and is used to calculate the rainwater distribution and the rain load on the surface of the dynamic rotating floating fan. The present invention can be used to calculate the rain load of static buildings, and can also be used to calculate the rain load of fans with dynamic characteristics, and solves the problem that the existing calculation method takes a long time in calculating the wind and rain load, the operation is cumbersome, and the calculation resources are consumed. Large, can only be calculated for static buildings and other issues.

Description of drawings

FIG. 1 is a schematic diagram of the present invention.

Figure 2 is a data graph of the size distribution of raindrops passing through the horizontal plane calculated by Best measurements.

Figure 3 shows the size distribution of the velocity of raindrops with different sizes measured by Gunn and Kinzer.

Figure 4 is a schematic diagram of a rotating reference frame (SRF).

Figure 5 shows the calculation result of the rainwater distribution on the fan surface.

Fig. 6 is a graph showing the results of the rain-induced pressure distribution on the fan blades.

Fig. 7 is a display diagram of the streamlines of the wind and rain phases after the calculation is completed.

Detailed ways

The present invention will be further described below with reference to the accompanying drawings.

In order to solve the many limitations of the existing calculation methods in calculating wind and rain loads, such as long time consumption, cumbersome operation, high computational resource consumption, and only static buildings can be calculated, the present invention provides a computational fluid dynamics-based method. A method for coupling the Euler polyphase model with multiple rotating frames of reference (SRF) and collision theory to calculate the rain distribution and rain loads on the surface of a dynamic rotating floating fan.

With reference to Figure 1, taking a floating fan installed and operating in an offshore area as an example, a method for calculating the rainwater distribution and rain load on the surface of a dynamic floating fan includes the following steps:

Step 1. Measure the required wind field data and construct the wind field;

First, measure the relevant data (wind speed, wind pressure, wind direction) of the wind field at the 200-meter boundary around the floating wind turbine, and use the measured wind field data as the boundary conditions for the numerical wind field to be constructed. The stable Reynolds-averaged Navier-Stokes (RANS) and KOmegaSST turbulence models are used to calculate the interaction process between the incompressible turbulent wind and the fan, and the information of the flow field after the interaction between the two can be calculated. The KOmegaSST turbulence model considers the transfer of turbulent shear stress on top of the standard k-ω model, but also considers low Reynolds numbers, compressibility, and shear flow propagation. The governing equations are as follows:

Among them, x _i and x _j represent the displacement in the i and j directions respectively; u _i and u _j represent the average wind speed in the i and j directions respectively; ρ _a represents the density of the air; p is the pressure of the air; K represents the turbulent kinetic energy ;ε is the turbulent dissipation rate; τ _ij is the Reynolds stress; μ is the air viscosity; μ _t is the air turbulent viscosity; G _K is the turbulent kinetic energy gradient generated by the average velocity; C _μ , C _2ε , C _1ε and σ _ε are all Constants; take C _μ =0.11, C _2ε =1.92, C _1ε =1.44 and σ _ε =1.21, respectively.

Step 2: Measure the rainfall intensity and inject the rain phase into the numerical wind field;

Measure the rainfall intensity R _h in the offshore area where the dynamic floating fan works. Based on the known rainfall intensity, determine which raindrops of different sizes are composed of raindrops and the falling speeds of raindrops of different sizes. Different continuous rain phases composed of raindrops of different sizes are injected into the top of the calculation domain of the stable wind field obtained after the calculation in step 1 to construct an Eulerian multiphase field, and the measured rainfall intensity related parameters (raindrop size, raindrop falling speed, rain fraction) as the boundary condition for the Euler polyphase field.

Different rain phases (one rain phase represents a raindrop of one size) are added to the top and the inlet of the steady-state wind field. In this study, a fixed rainfall intensity is selected, and each fixed rain intensity is selected correspondingly. A set of raindrop combinations of different sizes. For example, a rain intensity of 0.1mm/h is selected. Now a total of twenty rain phases are set. Each rain phase has a phase fraction and velocity vector. The diameters of the twenty rain phases range from 0.1 To 1 mm, the interval is 0.1 mm, the interval between 1 and 2 mm is 0.2 mm, and the interval between 2 and 7 mm is 1 mm. The selection of raindrop diameter is still based on the data map of the size distribution of raindrops passing through the horizontal plane calculated by Best measurement, as shown in Figure 2.

The boundary conditions of the rain phase are still controlled by two parameters, the raindrop end velocity V _k (d _k ) and the phase fraction α _k . The solution methods for these two parameters on the boundary conditions will be introduced below. Since the falling process of raindrops can be regarded as a process of first acceleration and then uniform velocity, the raindrops will maintain a constant final velocity before reaching the ground, so the initial velocity of the rain phase on the boundary conditions of the computational domain is the final velocity of the raindrops V _k (d _k ). Raindrop end velocity size measurements were performed by Gunn and Kinzer, as shown in Figure 3.

The size of the rain fraction on the boundary condition is also a fixed value, and the size is calculated by formula 6. d _k is the raindrop diameter of the k-th phase rain, and V _k (d _k ) represents the raindrop velocity of the k-th phase rain with a diameter of d _k .

等于零，当正常的风速速度矢量指向计算域时，相分数α_d的值等于零。利用此边界条件，雨和壁面(外墙壁、风机表面)之间的相互作用就可以不用被考虑，雨滴一旦到达壁边界就离开该区域，所以就可以忽略其他因素的能量损失，比如雨滴在冲击过程中的蒸发、飞溅、破裂等。For the setting of the boundary conditions of the rain phase on the fan surface, ground and outlet, the following self-made boundary conditions are used: the phase fraction gradient is equal to zero, when the normal wind speed velocity vector is pointed out from the computational domain, the gradient of the rain phase fraction is

equal to zero, the value of the phase fraction α _d is equal to zero when the normal wind velocity vector points to the computational domain. With this boundary condition, the interaction between the rain and the wall surface (external wall, fan surface) can not be considered, the raindrop leaves the area once it reaches the wall boundary, so the energy loss of other factors can be ignored, such as the impact of the raindrop Evaporation, splashing, cracking, etc. during the process.

Step 3. Use the rotating reference frame model;

After the calculation of the steady-state wind field is completed, the rain phase is injected into the calculation domain, and the fan starts to rotate, simulating the process of starting the 5MW fan in the wind and rain to maintaining the steady state. Since this study only focuses on the rotation of the fan in the wind and rain To maintain the relevant aerodynamic performance after the steady state, the SRF method (single rotating reference system method) commonly used in CFD is used, that is, the fan does not move, the coordinate system rotates, and the coordinates in the coordinate system are transformed, and then the computational domain is solved. . Different from the sliding grid, the SRF method does not have grid movement and exchange, which greatly saves the time cost of calculation. Figure 4 is a schematic diagram of the difference between the SRF and the slip grid.

Step 4: Solve the governing equation of the wind-rain coupling action;

The rain phase and the wind phase are combined, and the calculation adopts the assumption of one-way coupling, that is, the wind acts on the rain in one direction. This is a valid assumption because the volume ratio of rainwater in the air is less than 1*10 ^-4 . The rain phase is considered to be a continuum, and each rain corresponds to different levels of raindrop sizes. For each rain phase, after being injected into the wind, the following continuity and momentum equations when coupled with the wind phase are solved, as follows: Flow field information such as rain phase volume fraction (phase fraction) and velocity field can be obtained. Figure 7 shows the streamlines of the rain and wind phases in the flow field.

where α _k ′ is the rain phase fraction of the kth phase rain after the wind phase and rain phase are coupled in the computational domain; ρ _w is the raindrop density; g is the acceleration of gravity; C _d is the drag coefficient; Re _R is the relative Reynolds number, which is the Calculated as follows:

是风相速度矢量，

是雨相速度矢量；in,

is the wind phase velocity vector,

is the rain phase velocity vector;

Step 4. Calculate the surface rainwater distribution based on the observation data of rainfall events;

After obtaining the movement trajectory and control parameters of the rain phase, the distribution of rainwater on the outer surface of the building is obtained based on the distribution probability map of raindrops of different sizes measured by Best.

直接相关，两者计算公式如下：The parameter that defines the distribution of rainwater on the outer surface of the building under the action of wind and rain is the capture ratio, which is defined as the ratio of the rain intensity under the action of the wind to the rain intensity on the horizontal plane (ie, the conventional rain intensity). The size of the global capture ratio η is also related to the specific capture ratio of each rain phase.

Directly related, the two calculation formulas are as follows:

Among them, R _wdr (k) is the strength of wind on rain; u(k) is the final impact velocity vector of the k-th phase rain; f _h (d _k ) is the diameter of the k-th phase under the rainfall intensity R _h is the size probability distribution value of the rain phase of d _k on the horizontal plane, please refer to Figure 2 for details. Figure 5 shows the final calculation results of the rain distribution on the fan surface under the rainfall intensity of 5 mm/h.

Step 5: Calculate the rain load by collision theory.

The interaction process between rain and structures follows Newton's second law.

By the momentum theorem formula:

Among them, τ is the time for the rain to hit the wall, f(t) is the impact force vector of the rain phase, u is the combined velocity of the final velocities of all the rain phases before hitting the fan wall, and m is the rain phase mass.

So the impact force is:

Since the diameter of raindrops is generally small, and the final velocity before hitting the wall is relatively large, in order to simplify the calculation, take the collision time

And because the surface capture ratio of the fan is defined as: the ratio of the rain intensity under the action of the wind to the rain intensity on the horizontal plane, that is, the rain intensity on the surface of the fan is:

R=η×R _h (15)

Among them, η is the surface capture ratio of the wind turbine, and R _h is the horizontal rainfall intensity. Rain intensity, however, is equal to the volume of rainfall over a given area per unit time. Therefore, within τ time, the quality of rainwater on the fan surface micro-element area Δ _s is:

m=ρ _w ηR _h Δ _s τ (16)

The impact force of rain on the fan surface micro-element area Δ _s is:

F=ρ _w ηR _h Δ _s u (17)

Integrate the entire surface of the fan to calculate the rain load on the entire fan surface.

Figure 6 shows the radial rain-induced pressure distribution of fan blades A, B, and C. The selected operating conditions in the offshore area are horizontal wind speed of 6m/s, 11.4m/s, wind pressure of 50N, rotational speed of 12.1RPM, and rain intensity of 5mm/h.

The invention can be used to calculate the rain load of static buildings and the rain load of fans with dynamic characteristics, and solves the limitations of the current wind and rain conditions at home and abroad in the calculation of the rain distribution and the rain load of fans. and blank.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims (1)

1. A method for calculating the rainwater distribution and the rainwater load on the surface of a dynamic floating type fan is characterized by comprising the following steps:

step 1: measuring the wind speed, wind pressure and wind direction of a wind field around the dynamic floating type fan, and constructing a stable wind field calculation domain by using the measured data as boundary conditions;

the control equation for the wind field calculation domain at steady state is as follows:

wherein x is_i、x_jRespectively representing the displacement in the ith and the j directions; u. of_i、u_jRespectively representing the average wind speed in the ith and the jth directions; rho_aRepresents the density of air; p is the pressure of air; k represents turbulent kinetic energy; ε represents the turbulent dissipation ratio; tau is_ijRepresents the reynolds stress; μ represents air viscosity; mu.s_tRepresents the air turbulence viscosity; g_KRepresenting the turbulent kinetic energy gradient produced by the average velocity; c_μ、C_2ε、C_1εAnd σ_εAre all constants;

step 2: measuring rainfall R of offshore area of dynamic floating type fan working position_h(ii) a Determining the rainfall intensity R on the basis of the known rainfall intensity_hThe rains are composed of raindrops of different sizes and the falling speeds of the raindrops of different sizes; adding different continuous rain phases composed of raindrops with different sizes on the top and the inlet of a wind field calculation domain in a stable state to construct an Euler multiphase field, and measuring the sizes and the raindrops of the raindropsThe landing speed and the rain phase fraction are used as boundary conditions of the Euler multiphase field;

the raindrop falling process can be regarded as a process of accelerating first and then keeping constant speed, and the raindrop can keep a constant final speed before reaching the ground, so that the initial speed of the raindrop phase on the boundary condition of the calculation domain is the final speed V of the raindrop_k(d_k)，d_kDiameter of raindrop of kth-phase rain, V_k(d_k) Denotes the diameter d_kThe end-of-raindrop velocity of the kth-phase rain; rain phase fraction alpha_kThe calculation method comprises the following steps:

setting the boundary conditions of the rain phases of the surface of the fan, the ground and the outlet as follows: rain phase fraction gradient when normal wind speed velocity vector is indicated from the calculation field

Equal to zero, rain phase fraction alpha when normal wind speed velocity vector points to the calculation domain_kIs equal to zero; by utilizing the boundary condition, the interaction between rain and the outer wall and the surface of the fan can be not considered, and once the raindrops reach the boundary of the wall, the raindrops leave the area, so that the energy loss of other factors can be ignored;

and step 3: simulating the process from starting the dynamic floating fan in the weather to maintaining the stable state, and adopting a single rotating reference system method, namely, the fan is not moved, a coordinate system rotates and coordinate transformation is carried out on the amount in the coordinate system, so as to solve the calculation domain;

combining the rain phase and the wind phase, and adopting the assumption of unidirectional coupling in calculation, namely that the wind acts on rain in a unidirectional way; the rain phase is considered as a continuum, each rain corresponds to a different level of raindrop size; for each rain phase, after the rain phase is injected into wind, solving the following continuity and momentum equation when the rain phase is in single-term coupling with the wind phase to obtain rain phase fraction and speed field information;

wherein alpha is_k' calculating the rain phase fraction of the kth phase rain after the wind phase is coupled with the rain phase in the domain; rho_wIs raindrop density; g is the acceleration of gravity; c_dIs a coefficient of resistance; re_RThe relative reynolds number is the relative reynolds number,

is the vector of the velocity of the wind phase,

is the rain phase velocity vector;

and 4, step 4: calculating to obtain surface rainwater distribution based on rainfall event observation data;

the parameters defining the distribution of rain on the external surface of the building under the action of wind and rain are capture ratios, which are defined as the ratio of the intensity of rain under the action of wind to the intensity of rain on the horizontal plane, and the size of the global capture ratio eta is equal to the capture ratio eta specific to each rain phase_dk(k) The two are directly related, and the calculation formulas are as follows:

wherein u (k) is the final collision velocity vector finally calculated by the k-th phase rain; f. of_h(d_k) As intensity of rainfall R_hLower, the k-th phase diameter is d_kThe size probability distribution value of the rain phase on the horizontal plane;

and 5: calculating the surface infinitesimal area delta of the fan_sThe upper rainwater collides with the impact force F of the fan, and then the integral of the whole surface of the fan is obtained to obtain the surface rain load of the fan;

fan surface infinitesimal area delta_sThe impact force of the upward rainwater collision fan is as follows:

F＝ρ_wηR_hΔ_su

wherein u is the resultant velocity of the final velocities of all the rain phases before impacting the wall surface of the fan.

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